Rapid aging and disassembly of actin filaments from two evolutionary distant yeasts

Similarities and differences in the self-assembly of actin filaments from different species inform our understanding of its evolution. However, this basic knowledge is largely incomplete. Here, we systematically characterize assembly kinetics for actin from two yeast species that are five hundred million years apart in evolution, Saccharomyces cerevisiae and Schizosaccharomyces pombe, and compare them to the well-studied rabbit muscle actin from which they diverged a billion years ago. We find that, in the ATP state, both yeast actins behave strikingly like mammalian actin at filament barbed ends. In contrast, yeast actin filaments in both the ADP·Pi and the ADP states depolymerize several-fold faster than their mammalian counterparts, and they release inorganic phosphate over 20-fold faster. We show that the absence of methylation on histidine 73 largely accounts for this faster aging of yeast actin filaments. We also reveal biochemical and mechanical differences between the actins of the two yeasts. Our findings suggest that actins are more diverse and biochemically specialized across species than previously recognized.